Inorganic metal insulation



Patented Apr. 25, 1933 V UNITED STATES PATENT OFFICE EMIL RUPP, OF BERLIN-FROHNAU, GERMANY, ASSIGNOR 'I'O GENERAL ELECTRIC COM- PANY, A CORPORATION OF NEW YORK INORGANIC METAL INSULATION No Drawing. Application filed March 23, 1931, Serial No. 524,772, and in Germany April 7, 1930.

8 coating.

It is known that fluorine compoundsof metals are good insulators. These fluoride compounds are, in addition, very resistant, and in contradistinction to most chlorides are 10 not very solublein water. They also crystallize in much smaller crystalline bodies than chlorides and adhere better to metals.

The present invention relates to a method which makes use of these qualities of fluorides to produce a highly valuable insulating layer on metals. The method consists generally in bringing the metal in contact with a fused fluoride compound so that a thin layer consisting of the fluorine compound of the metal and of the fluorine compound of the fusion is formed on the metal. For example, the metal is immersed in the fusion of the fluoride compound until it has taken on the temperature of the fusion. The metal is then:-.withdrawn and allowed to cool in a non-oxidizing atmosphere. The metal thereby becomes coated with a thin layer which consists of the fluoride compound of the metal and of the fluoride compound of the fusion and is crystallized in very fine grains. It is obvious that the metal employed should have a melting point higher than the fluoride compound into which it is introduced.

The production of an insulating layer on copper wire may be given as an illustrative example of the method according to the invention. Copper wire is slowly drawn through fused potassium fluoride. An atmosphere of a non-oxidizing gas, for example, carbon dioxide, is maintained over the fusion. After being withdrawn the copper wire is surrounded by a thin layer composed of copper fluoride over which is deposited potassium fluoride as a further thin layer. The crystalline structure is of such fine grain that the wire can be bent without the layer cracking.

The fluoride layer can also be obtained by electrolysis of the fused fluoride compound.

The fluorine separating during electrolysis combines with the metal.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A method for producing an insulating layer on metals having a melting point higher than alkaline fluorides which comprises contacting the metal with a fused alklaine fluoride until it has assumed the temperature of the latter and a thin, adherent layer consisting of the fluorine compound of the metal and of the fluorine compound of the fusion is formed on the metal, and cooling said coated metal outside of the bath in a non-oxidizing atmosphere.

2. A method for producing an insulating layer on metals having a melting point higher than alkaline fluorides which comprises conductin the metal through a bath of a fused alkaline fluoride at a rate such that the metal .has assumed the temperature of the bath before emergence therefrom and cooling said metal after withdrawal from said bath in a non-oxidizing atmosphere.

3. A method for producing an insulating layer on a copper conductor which comprises slowly drawing said conductor through a bath of fused alkaline fluoride while maintaining a non-oxidizing atmosphere over said bath.

4. A method for producing-an insulating layer on copper which comprises maintaining the copper in contact with a bath of fused alkaline fluoride until it has assumed the temperature of the latter and cooling the coated metal in a non-oxidizing atmosphere outside of the bath..

5. A method for producing an insulating layer on copper which comprises conducting the copper through a bath of fused potassium fluoride at a rate such that the metal has assumed the temperature of the bath before emergence therefrom and cooling the coated copper after withdrawal from said bath in a non-oxidizing atmosphere.

In witness whereof, I have hereunto setmy hand.

EMIL RUPP. 

